I just installed v4.80. The installation seems to have gone just fine; I chose for the location of the files to be ProgramFiles.
I can't open Pegasus at all for some reason, neither the regular version nor the admin version. The logo/start screen will pop up for less than half a second before disappearing.
I tried restarting my laptop, looking for any Pegasus processes in the task manager to kill them but there's nothing.
Anybody else got this issue?

Pegasus Mail will not work when installed to a ProgramFiles directory if Windows 10 or 11. In those OSes, the ProgramFiles directory is a system protected location. The OS prevents modification of files required for Pegasus Mail to function.

Uninstall it. Remove the directory \ProgramFiles\Pmail.

Reinstall somewhere else. I suggest installing to the default C:\PMAIL. Installing to this default location will make it easier to troubleshoot if needed.

Might also want to make sure you have a directory C:\TEMP that has read/write access for all users. Windows has now move the TEMP directory to each users section, but bearhtml sometimes creates files in the old C:\TEMP directory, so if it doesn't exist and has read/write access for users can also cause issues. Using default C:\PMAIL is the BEST.

Good Luck.